Prediction of stable C7/12 and metastable C4/7 commensurate solid phases for He 4 on graphite

Jeonghwan Ahn, Hoonkyung Lee, Yongkyung Kwon

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Abstract

Using a substrate potential described by a pairwise sum of empirical He4-C interatomic potentials, we have performed path-integral Monte Carlo calculations for He4 adatoms on graphite. It is found that a second-layer commensurate structure is not stable above an incommensurate first-layer triangular solid. This is consistent with the conclusion of the previous theoretical study of Corboz et al. [Phys. Rev. B 78, 245414 (2008)PRBMDO1098-012110.1103/PhysRevB.78.245414] that was based on a laterally averaged one-dimensional potential. On the other hand, we observe a new stable C7/12 commensurate solid in the first He4 layer at the areal density of 0.111 Å-2, which is close to the second-layer promotion density. This high-density commensurate solid exhibits a 12×12 structure registered to the graphite surface that is not disrupted by the development of the second He4 layer. Furthermore, a second-layer 4/7 commensurate structure relative to the first-layer C7/12 solid is found to be at least metastable, opening the possibility of two-dimensional supersolidity.

Original languageEnglish
Article number064511
JournalPhysical Review B
Volume93
Issue number6
DOIs
StatePublished - Feb 17 2016
Externally publishedYes

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